1. Field of the Invention
The present invention relates to the qualitative and quantitative chemical analysis of drugs, particularly to a potentiometric device and method selective for pioglitazone that may be used detection and measurement of the concentration of the drug for quality control in the manufacture of the drug, etc.
2. Description of the Related Art
A potentiometric sensor is a type of electrochemical sensor that may be used to determine the presence and concentration of substances in a gas or solution. These sensors measure the electrical potential of an electrode when no current is flowing. The signal is measured as the potential difference (voltage) between the working electrode and the reference electrode. The working electrode's potential must depend on the concentration of the analyte in the gas or solution phase. The reference electrode is needed to provide a defined reference potential.
Potentiometric sensors typically use an ion selective electrode (ISE). The voltage between a reference electrode and the ISE exposed to an analyte solution can be measured, and since this voltage is related to the activity of the analyte by the Nernst equation, the unknown concentration of the analyte can be computed. There are several different types and configurations of ion selective electrodes, with and without internal reference solutions. The ISE usually uses a semipermeable membrane or selectively permeable membrane that is selective for the cation or anion of interest. One type of membrane used in an ion selective electrode is a polymer membrane. The polymer membrane includes a polymer matrix, often of poly (vinyl chloride) (PVC), that is doped with an ionophore (an organic ion exchange agent). The membrane also may include a plasticizer to keep the polymer soft and amorphous so that the ion of interest can be transported between the aqueous analyte solution and the ionophore embedded in the polymer matrix. The plasticizer may also affect the dielectric constant of the polymer membrane. Plasticized polymers used for ISE membranes are sometimes described as viscous liquids and referred to in the literature as liquid membranes.
One type of ionophore used in an ISE is an ion-pair ionophore. The potential measured by an ion-pair sensor electrode is dependent upon the relative attraction and repulsion forces of the ion-pair complex and the ionic species of the analyte of interest. Pioglitazone ([(±)-5-[[4-[2-(5-ethyl-2-yridinyl)ethoxy]phenyl]methyl]-2,4-]thiazolidinedione) hydrochloride is an oral anti-hyperglycemic agent that is used in the treatment of type 2 diabetes. A testing method that is quick, simple, and relatively inexpensive for detecting and measuring the concentration of pioglitazone in pharmaceutical manufacture and in biological fluids for ensuring therapeutic levels of the unmetabolized drug is desirable.
Thus, a potentiometric device and method selective for pioglitazone solving the aforementioned problems is desired.